Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1056 AM EST Fri Feb 01 2019 Valid 12Z Mon Feb 04 2019 - 12Z Fri Feb 08 2019 ...Warmed Central-Eastern U.S. Flips Back to Cold and Offers Several Winter Storm Threats... ...Cold and Stormy Pattern for the West... ...Guidance/Predictability Assessment... The WPC medium range product suite has been derived from a composite of the 06 UTC GFS/GEFS mean and 00 UTC ECMWF/ECMWF ensemble mean days 3-5 (Mon-Wed). These forecasts in particular now seem quite well clustered, bolstering forecast confidence. Increasing forecast spread days 6/7 are mainly aligned with uncertain energy digging into the western U.S. versus ejection into the flow over the central and eastern U.S. Accordingly, just used the 00 UTC ECMWF ensemble mean and 06 UTC GEFS mean days 6/7 amid growing uncertainty, for now applying extra weighting to the blend toward the ECMWF ensembles that maintains better WPC continuity. ...Weather Highlights/Hazards... A much milder weather pattern will be prevalent across much of the central and eastern U.S. this weekend into early next week as flow from the Gulf of Mexico advects higher humidity over the region. Record mild temperatures may precede an approaching front from the Midwest to the Northeast with anomalies of about +10 to +30 (generally above freezing to the north and 50s/60s in the Mid-Atlantic. Western Atlantic low pressure may delay high pressure erosion over the eastern states Monday and offer some potential for showers to work onshore into the eastern Carolinas. A couple of well defined low pressure systems upstream are meanwhile expected to track across the Plains and Midwest/Great Lakes before lifting into eastern Canada next week. These have the potential for significant snow and winds to the north of the main surface lows across the northern Plains and Upper Midwest/Great Lakes/Northeast in the broadening arctic airmass. Later period frontal progression into the East is now more slowed by a building mean ridge aloft and with a recent model trend to dig energy robustly into the West. This allows cooled high pressure to hold longer from the Northeast into the Mid-Atlantic. Warm sector showers/thunderstorms are likely to focus from the mid-South to the OH Valley/Appalachians and there is some risk of locally heavy amounts. A guidance trend toward development of a more amplified western U.S. mean mid-upper level trough next week is complicated by changing shortwave trough systems to dig/reinforce the main longer wave feature. That said, forecast confidence is above average in the overall idea that much of the West will become increasingly cold and stormy next week with passage of multiple systems/height falls. This includes valley rain and higher elevation snow (with lowering snow levels), wind, and cooler temperatures from Oregon/southern Idaho southward and southeastward. To its north will be a slowly advancing arctic front that will bring well below average temperatures to much of Montana where highs will struggle to get to zero (about 20-45 degrees below average) that will bleed into the Dakotas as well. The Sierras will see another round of snow with more than a foot likely. Schichtel WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities are found at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4